The invention relates to a constant velocity universal ball joint. The joint has an outer joint part with substantially longitudinally extending circumferentially distributed ball tracks and an inner joint part with substantially longitudinally extending circumferentially distributed ball tracks. The tracks are arranged in pairs radially opposite one another and jointly receive a torque transmitting ball. A cage, which receives the balls in circumferentially distributed windows, holds the balls in a common plane and which, upon articulation of the axes of the outer and inner joint parts, guides the balls on to the angle-bisecting plane, with the outer joint part being produced with surfaces between the individual tracks, which, if viewed in the axial direction, constitute undercut-free inner surfaces. At least three cage securing elements are inserted into the outer joint part in each case between two ball tracks, are connected to the outer joint part and form cage contact and cage guiding faces which counter-act any axial movement of the cage out of the outer joint part. The balls are able to move into gaps between the securing elements.
The subject of the invention can be applied to different types of constant velocity universal ball joints, especially to so-called RF joints (Rzeppa fixed joints) and the so-called UF-joints (undercut-free joints). Joints of this type are described in F. Schmelz et al, "Gelenke und Gelenkwellen: Berechnung, Gestaltung, Anwendungen" (Joints and driveshafts: calculation, design, applications), Berlin, Heidelberg, New York 1988 under said headings. In these joints, the cage is not or not entirely controlled by the shape of the cage guiding faces, but primarily by the shape of the ball tracks in the outer joint part and inner joint part, with the centre lines of the ball tracks deviating from one another, but extending symmetrically to a plane defined by the ball centres when the joint is in the extended position.
A joint of the above type is illustrated DE 32 33 759 C 2 where the securing elements are provided in the form of bolts threaded almost radially into the outer joint part. Both the method of preparing the outer joint part for receiving the said securing elements and setting the play are cost- and time-consuming operations. As the outer joint part requires a sufficient amount of material to receive the securing means, the outer joint part has to have a relatively great axial length with reference to the plane extending through the ball centres of an extended joint, which length limits the joint articulation angle in respect of the possible freedom of movement of the connected shaft when the joint is in an articulated condition. A joint of the above type is also shown in DE 24 30 027 B1 in which case the securing means are inserted axially and secured jointly by a securing ring inserted into an annular groove in the outer joint part. The securing ring obstructs the possible ball travel in the tracks in the outer joint part so that a limited joint articulation angle has to be accepted. In the same way, the securing ring limits the articulation angle in respect of the possible freedom of movement of the connected shaft when the joint is in the articulated condition. The cage, in this case, is supported inside the outer joint part on resiliently held further stop means. If the joint which is to act as a fixed joint is subject to greater thrust forces, such a solution is unsuitable because the joint function of an axially fixed joint centre is not complied with.
Furthermore, a joint of a similar type is known from DE 36 26 998 A 1 where the only securing element is a securing ring inserted into an inner groove in the outer joint part. It is not possible to adjust the play at the cage for the purpose of compensating for manufacturing tolerances. The securing ring inserted into the outer joint part after the inner joint part including the cage and balls, have been assembled in the form of a complete unit is disadvantageous in that the articulation angle of the joint is limited considerably. On the one hand, the ball travel in the tracks is limited by the inserted securing ring and on the other hand, the securing ring forms a stop for a shaft associated with the inner joint part.
A further joint of a similar type is known from DE 25 22 670 B 1 in which case the securing element consists entirely of an annular member positioned on the end face of the outer joint part, having individual inwardly deformed tongues and held by a plate metal cap. Again, the annular member restricts the articulation angle of the joint in that it forms a stop for a shaft associated with the inner joint part when the joint is articulated. As the annular member has to be pre-formed, an axial adjustment of play is not possible. The individual tongues are not able to accommodate greater axial drag forces so that the joint function as a fixed joint with a fixed joint centre is not observed.
It is the object of the invention to provide a joint of the above type in the case of which the maximum articulation angle is not adversely affected by the securing elements for the cage and where the securing elements may be used for setting the axial play at the cage. The objective is achieved in that the securing elements are formed by independent wedges which are axially inserted into the annular gap between the outer joint part and the outer face of the cage, which are fixed especially welded to the outer joint part and which, with a set axial play, hold the cage in the outer joint part by means of contact in contact points A. In the case of a joint with six balls for example, it is possible for three securing elements with two ball tracks arranged between two of them, respectively, to be uniformly circumferentially distributed.
With this design it is possible, in an advantageous way, prior to fitting the securing elements, to insert the cage into the outer joint part with the cage axis being positioned coaxially relative to the axis of the outer joint part, with the securing elements then being inserted into, and connected to the outer joint part. In this way, the usually complicated operation of introducing the cage into the outer joint part is avoided. As explained above, the inner joint part and cage may be preassembled and jointly introduced coaxially into the outer joint part. As the tracks are axially undercut-free towards the aperture of the outer joint part, the balls,too, may form part of the assembled group of cage and inner joint part, which then, in its entirety, is axially introduced into the outer joint part. At the same time, as a result of the method of assembly, the entire joint may be adjusted so as to be axially play-free or comprise a small predetermined amount of play independently of the production tolerances.
According to a preferred embodiment, the radii of curvature of the tracks are axially offset oppositely relative to a plane E.sub.K through the amount of ball centres of the extended joint, the amount of offset O.sub.1 of the inner joint part being permitted to deviate from the offset O.sub.2 of the outer joint part. When the joint is articulated, the cage is controlled primarily by means of the ball tracks and balls so that it is possible for the cage to be relatively light with a uniform wall thickness.
A first variant of the invention includes the inner surface between the tracks in the outer joint part forming cage contact and cage guiding faces against which the cage, in contact points E, is supported axially inwardly on the outer joint part. This constitutes a particularly simple way of axially securing the cage. As already described, the securing elements may be welded on while directly contacting the cage or after a small axial play has been set after a reference position has been found due to the securing elements axially contacting the cage.
In a further embodiment of the above-mentioned variant, the inner joint part is axially inwardly supported in the outer joint part by means of its outer face on the inner face of the cage and thus indirectly by means of the cage. It is axially outwardly supported in the outer joint part by means of its tracks on the balls and thus indirectly by means of the balls and cage and by means of the securing elements.
By deviating from the above, the inner joint part may be axially inwardly and outwardly supported in the outer joint part, in each case by means of its outer face on the inner face of the cage and thus indirectly by means of the cage and securing elements only. With this variant, no support is provided by the cage windows.
Irrespective of the shape of the axial support means, the balls, with the cage being held in the outer joint part in a play-free way, are to be held in the tracks in the outer joint part and inner joint part in a radially nearly play-free way.
In order to avoid any edge carriers after the cage has been fixed, after the securing elements have been inserted and secured, it is proposed that the centres M.sub.1, M.sub.2 of the cage contact and cage guiding faces at the securing elements and in the outer joint part are axially offset in opposite directions relative to a plane through the ball centres of the extended joint radii R.sub.1, R.sub.2 are greater than the radius R of the outer face of the cage.
A second variant of the invention is characterised in that the inner surface between the tracks in the outer joint part provides a radial play S.sub.3 relative to the outer surface of the cage. Also the inner surface of the cage is in contact with contact points D of outer surfaces of the inner joint part positioned between the tracks. Further the cage, by means of the cage windows, is axially inwardly supported on the balls on contact points B on the flanks positioned towards the aperture of the outer joint part, said balls in turn are supported in contact points C.sub.1, C.sub.2 on the tracks of the outer joint part and of the inner joint part.
In this case, too, as explained above, assembly may lead to there being no axial play at all or it may be used for setting a desired amount of axial play, in which case again the axial play is initially set to zero in order to find a reference position. When there is no axial play, there is also no radial play for the balls because for support reasons the balls have to contact the tracks. Such contact may take place on the track base, but depending on the cross-sectional shape of the tracks, a double ball contact at the flanks of the respective tracks is also possible.
According to a further embodiment of the invention it is proposed that between the inner surface of the cage and the outer surface of the inner joint part, at the end positioned towards the aperture O of the outer joint part, there is provided a radial play S.sub.1. Furthermore, it is proposed that when the balls contact the tracks on contact points C.sub.1, C.sub.2 and the cage windows in the contact points B, there exists an axial play S.sub.2 relative to the flanks of the cage windows positioned towards the inside of the outer joint part. In this way it is possible to increase the size of the surface parts at the inner joint part and cage that remain unmachined. According to a further embodiment advantageous for both variants, the inner surface of the outer joint part, in the region of a plane E.sub.K through the ball centres of the extended joint and beyond said plane into the inside of the outer joint part, includes an inner cylindrical portion Z. In this way it is possible to prevent the cage from moving out radially in the course of the axial assembly operation described above on several occasions because the cage comes to rest against said the inner cylindrical face. Furthermore, the tendency of the outer joint part to deform under torque is limited because the outer joint part is supported by the inner cylindrical face on the cage.
According to a preferred embodiment, the ball tracks in the outer joint part and inner joint part, if viewed from the aperture end of the outer joint part, are axially undercut-free, thereby achieving the advantage during assembly in that the balls, too, may be pre-fitted together with the inner joint part and cage and that the assembled unit may be axially inserted into the outer joint part before the securing elements are finally fitted. As the length of the cage windows in the circumferential direction is determined by the path of the balls relative to the cage when the joint is articulated, which path increases with an increasing articulation angle, a joint in accordance with the invention permits the length of the windows in the circumferential direction to be limited. This means that the length of the windows in the circumferential direction merely needs to correspond to the path which is covered by the balls relative to the cage in the circumferential direction when the joint rotates at the operating angle. This means that there is no need for articulating the axes of the inner joint part and outer joint repeatedly until an assembly angle is reached at which a cage window freely emerges from the outer joint part to allow a ball to be inserted radially.
The individual securing elements allow the amount of play to be adjusted relative to the cage, at which amount of play the axial securing means may be adjusted individually and independently, thereby also achieving uniform load-bearing conditions between the surface of the securing elements and the outer surface of the cage.
According to an advantageous embodiment, the securing elements include simple wedges which are introduced into an annular surface of the outer joint part, which are made to contact the previously inserted cage and which, optionally prior to being connected to the outer joint part, are withdrawn by the amount of axial play to be set. The inner faces of the wedges facing the cage may include an inner curvature or an inner wedge shape in order to establish contact with the outer spherical cage.
To facilitate assembly, the inside of the outer joint part, in a further embodiment, may be provided with pockets or recesses which are engaged by the securing elements in a circumferentially form-fitting way. In this way, the circumferential position of the securing elements is observed more easily during assembly.
In a further advantageous embodiment, the recesses are designed in such a way that the securing elements, prior to being connected to the outer joint part, are movable therein so as to be axially and/or radially guided. A preferred design of such recesses refers to longitudinal grooves arranged at an angle relative to the axis, and the securing elements may be wedge-shaped, as mentioned above.
In a particularly advantageous embodiment, the outer joint part is a formed plate metal part with a substantially constant wall thickness, and it is particularly advantageous for such a part produced by deep-drawing to be axially completely undercut-free, with the individual welded-in axial securing elements axially supporting the cage.